The present invention relates to a sealed container and a method and apparatus for testing the integrity of the sealed container and more particularly relates to an evacuated container and a method and apparatus for testing an evacuated container.
In many applications it is desireable to evacuate a container and to hermetically seal the container and maintain the evacuated and sealed nature of the container over a long period of time. An example of such a container is a vacuum insulation panel such as those disclosed in U.S. Pat. Nos. 4,668,551 and 4,681,788. Such vacuum insulation panels are suggested for use in refrigerator/freezer cabinet walls to reduce heat load on the refrigeration system; thereby achieving substantial product energy usage reductions. Successful application of vacuum insulation panels in the refrigerator/freezer walls require that an acceptable vacuum level inside the panel be maintained for twenty years or longer. Any loss of vacuum beyond acceptable limits would seriously degrade the product performance. Once the vacuum insulation panels are placed into the refrigerator/freezer walls, it would be extremely difficult to determine the integrity of the insulation system (other than catastrophic failures), short of testing every product for energy consumption. Since there are more than ten million refrigerators produced in the United States on an annual basis, such testing would be impractical. Further, even if a defective panel were located by such testing, replacement of the panel would cause severe damages, if not destruction, of many components of the refrigerator/freezer.
Therefore there is a need to provide a technique to test vacuum insulation panels before they are applied to the refrigerator/freezer cabinets. There is a similar need to provide a technique to test other types of evacuated containers. Since such vacuum insulation panels need to be manufactured in very large numbers at very high speeds, any test technique has to be accurate enough to test the vacuum insulation panels in a very rapid manner.